Near continuous data protection without using snapshots

ABSTRACT

One example method includes performing delta operations to protect data. Each delta generated by a data protection operation includes data. The deltas are stored in a delta queue, when moving a current replica to another point in time represented by the selected delta in the delta queue, the deltas are processed so that all relevant data can be applied in a batch. This ensures that when the same extents are represented in multiple deltas, only the oldest version is applied to the replica volume to move the current replica to the selected point in time.

FIELD OF THE INVENTION

Embodiments of the present invention generally relate to data protection operations including backup operations. More particularly, at least some embodiments of the invention relate to systems, hardware, software, computer-readable media, and methods for data protection operations, including backup operations with low recovery point objective (RPO).

BACKGROUND

Backup operations are often performed using snapshot technologies. Generally, a snapshot of data is a copy of the data at a particular point in time. Performing a snapshot operation, however, can impact performance of a computing system because of the need to stun or quiesce the computing system. Snapshots, including snapshots used with virtual technologies, are used to freeze the virtual machine for data protection purposes. The IO (Input/Output) interruption caused by taking a snapshot may limit the number of snapshots that can be performed. Stated differently, some backup technologies may suffer from an RPO that is too large. Improvements are needed to further reduce RPO on the production side when protecting data.

Improvements in backup technologies are also needed on the target side. More specifically, even if snapshot technologies have a high RPO, performance at the target site is not typically an issue. The issue on the target site is that a limited number of snapshots or point in time backups are available. In other words, the number of snapshots available at the target site could be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which at least some of the advantages and features of the invention may be obtained, a more particular description of embodiments of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, embodiments of the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which:

FIG. 1 discloses aspects of change block tracking for data protection operations;

FIG. 2 discloses aspects of bit logic performed during data protection operations including delta operations;

FIG. 3 discloses aspects of a data protection system configured to perform data protections including delta operations;

FIG. 4 discloses aspects of a flow diagram for a data protection operation or a delta operation;

FIG. 5 discloses aspects of performing bit logic when transmitting processing a primary bitmap during a delta operation;

FIG. 6A discloses aspects of a data protection system configured to perform at least replication operations using delta;

FIG. 6B discloses aspects of a delta's format and aspects of a delta queue;

FIG. 7A discloses aspects of metadata and data associated with deltas;

FIG. 7B discloses aspects of generating a point in time replica using deltas;

FIG. 8A discloses aspects of a delta queue that allows a volume to be rolled forward and backward in time;

FIG. 8B discloses aspects of rolling a replica volume forward in time;

FIG. 8C discloses aspects of rolling a replica volume backward in time;

FIG. 8D discloses aspects of a method for rolling a replica volume forward using deltas;

FIG. 8E discloses aspects of a method for rolling a replica volume backwards using undo deltas; and

FIG. 9 discloses aspects of a computing device or of a computing system.

DETAILED DESCRIPTION OF SOME EXAMPLE EMBODIMENTS

Embodiments of the present invention generally relate to data protection operations. More particularly, at least some embodiments of the invention relate to systems, hardware, software, computer-readable media, and methods for data protection operations including near continuous data protection operations, delta operations, backup operations, replication operations, and the like.

Example embodiments of the invention relate to a backup operation that can reduce RPO for data protection to seconds. Embodiments of the invention are described in the context of virtual machines (VMs), but can be implemented using containers, physical machines, and the like or in situations where IOs (Input/Outputs) can be intercepted in flight.

Snapshot operations are performed by stunning or quiescing a virtual machine (or other device/system) and then taking a snapshot of the virtual machine (or its volumes). Stunning the virtual machine, however, interrupts the performance of the virtual machine and the associated IO. As a result, the RPO for snapshot operations for a virtual system or machine can be on the order of hours.

Snapshots can be improved by taking differentials or deltas (referred to herein as deltas). A delta relates to changes that have occurred since a previous operation, such as a previous delta operation or a previous full snapshot operation. Deltas are distinct from a full snapshot, but allow a backup to be created for a specific point in time. The point in time backup can be generated by combining one or more deltas and/or a base snapshot or base backup. Generating conventional deltas, however, is complex and requires both a significant number of bitmaps and a data log that stores some of the changes associated with the deltas. These bitmaps and data log are needed at least to manage the IOs that may occur after a command to perform a backup or delta operation has been received. Although deltas can reduce the RPO compared to the RPO of full snapshots, conventional deltas are complex to generate and manage. Further, performing conventional deltas requires multiple passes of the relevant bitmaps and related volumes and/or logs. Embodiments of the invention thus relate to improved deltas and improved delta operations.

Embodiments of the invention include a one-pass mechanism that allows the RPO to be reduced to the order of seconds and uses two maps. Embodiments of the invention, by way of example only, may reduce the RPO to 10 seconds or less, 5 seconds, or less, or the like. By reducing the RPO to the order of seconds, a continuous or near continuous stream of deltas can be exported to enable near continuous data protection (CDP). The deltas can be generated at a cadence of a few seconds. Each delta may include changes to a virtual machine or the virtual machine's volumes since a previous operation. Because each delta represents a point in time, deltas separate by a few seconds provide near continuous protection.

Embodiments of the invention generate deltas using a filter. A splitter is not required to generate deltas according to embodiments of the invention. Generating deltas without a splitter reduces overhead, reduces complexity, and allows RPO to be reduced to the order of seconds.

Embodiments of the invention are discussed with reference to bitmaps. A bitmap is an example of a map. Other maps used to track changes or for other purposes may include, by way of example only, a list, a linked list, an array, or the like. Any structure that allows an area of a volume or disk to be marked as changed may be used in embodiments of the invention.

FIG. 1 discloses aspects of a changed bit tracking (CBT) bitmap. The bitmap 102, in this example, includes a plurality of entries. Each entry corresponds to an extent on the volume 110. Each extent corresponds to a portion of the volume 110. The extents can be of any desired size. When data is written to the volume 110, however, the data is not necessarily the same size as the extent. Thus, a single write may involve one or more extents. However, the bitmap 102 tracks dirty areas based on extents regardless of IO size in some embodiments. In one example, the bitmaps may include dirty and clean bits. A dirty bit represents that the corresponding extent or location has changed and needs to be backed up. A clean bit represents that the corresponding extent or location has not changed and does not need to be backed up. The following discussion considers a bit set to 1 to be a dirty and a bit set to 0 to be clean. However, a 0 could represent a dirty area and a 1 could represent a clean area.

When an IO 104 is received and being written to a location (or address) 108 on the volume 110, the bitmap 102 is marked. More specifically, the entry in the bitmap 102 corresponding to the extent that includes the location 108 is marked. The bitmap 106 is an example of the bitmap 102 after writing the IO 104 to the volume 110. In the bitmap 106, the entry 112 has been marked (e.g., set to 1).

By marking the entry 112, it is understood that the extent corresponding to the entry 112, which includes the location 108, is dirty (not yet backed up). When a backup operation is performed, it is only necessary to backup the extents corresponding to the marked entries in the bitmap 106. When generating a delta during a delta operation, the extents corresponding to the marked entries in the bitmap are transferred together as a delta or as a differential.

More specifically, each entry in the bitmap 102 represents a fixed size extent (e.g., 64 KB) and each entry in the bitmap 102 corresponds to a different extent. Thus, the first entry in the bitmap 102 corresponds to the first extent in the volume 110. The second entry in the bitmap 102 corresponds to the second extent in the volume 110, which is usually adjacent to the first extent. The index of the bit or entry in the bitmap 102 correlates to a corresponding extent in the volume 110.

When the IO 104 only overlaps with a portion of an extent, the corresponding entry in the bitmap 102 is still marked. When the IO 104 is written to the volume 110, the location to which the IO 104 is written may overlap with more than one extent. Thus, a single IO 104 may result in more than one bit being set in the bitmap 102. The relationship between the bitmap 102 and the volume 110 may depend on the size of the bitmap and the size of the volume 110.

For example, a bitmap having a size of 256 KB (2 M bits) and a volume size of 64 TB means that each bit represents an extent of 32 MB. Smaller volumes mean that each bit (assuming the same bitmap size) represents a smaller extent size. By way of example and not limitation, extent sizes, for a 256 KB bitmap and typical volume sizes, are between 8 KB and 128 KB.

FIG. 2 discloses aspects of bit-level logic used when generating deltas for transmission to a target site or other consumer. Generally, FIG. 2 illustrates a primary bitmap 210 and a secondary bitmap 220. The primary bitmap 210 is tracking changes to the volume 224 since a last backup or delta operation in this example.

This example illustrates the logic that is applied to an IO 222 in the context of generating deltas. The IO 222 is processed based on the status of the relevant bits in the primary bitmap 210 and the secondary bitmap 220. The relevant bits depend on the address of the IO 222 or the extents to which the IO 222 is written. The delta includes a copy of the extents that are marked in the primary bitmap 210 and thus include changes to the volume 224. Copies of these extents, which includes changes since the previous delta operation, are included in the delta and transmitted for storage.

In this example, changes are tracked 250 in the primary bitmap 210. Each time an IO 222 is sent to the volume 224, the appropriate bit (or bits) is marked in the primary bitmap 210. When a backup or delta operation is initiated 252, new changes to the volume 224 are tracked in the secondary bitmap 220. Thus, the primary bitmap 210 is frozen in time with respect to new IOs one the command for a delta operation is received or initiated. Once the delta is generated and processed, the secondary bitmap 220 becomes the primary bitmap and changes are tracked until another backup or delta operation is initiated. Then a new secondary bitmap is generated or the original primary can be used as the secondary bitmap.

Thus, incoming IOs are marked in the primary bitmap 210. When a backup is requested, the bit logic is applied to subsequent IOs. More specifically, the bit logic is applied to the entries in the primary and secondary bitmaps corresponding to the location of the incoming IO. If an IO impacts more than one bit, each pair of bits in the primary and secondary bitmaps are considered independently. There are four possibilities as illustrated by the primary bitmap 210 and the secondary bitmap 220. The four possibilities are (primary bitmap, secondary bitmap) or (0,0), (1,0), (0,1), and (1,1).

Each of these possibilities is represented in the bitmaps 210 and 220. The bitmaps 210 and 220 represent 4 different extents and each extent represents one of these scenarios.

If the IO 222 is received for a location in an extent corresponding to the index 260 after the delta operation is initiated, the bits are (0,0) as indicated by bit 202 and 212. Because the bit 202 is zero, this indicates that the IO 222 is not included in the delta being generated. In other words, the extent corresponding to the index 260 is not dirty and does not need to be included in the delta being generated. Because the bit 212 in the secondary bitmap is 0, the bit 212 is changed to a 1 or marked in the secondary bitmap 220. The IO 222 then proceeds to the volume 224. This ensures that the extent corresponding to the index 260 in the secondary bitmap 220 will be included in the subsequent delta.

The next scenario is when the IO 222 is received for the extent associated with the index 262. In this scenario, the bit 204 is 0 and the bit 214 is 1−(0,1). Because the bit 204 is 0, this indicates that the extent corresponding to the index 204 is not included in the delta being generated. Because the bit 214 is a 1, the IO is allowed to proceed. Even if the IO 222 in this scenario is writing to an extent that has already received a write, the goal is to identify extents that need to be copied during the next delta operation using the secondary bitmap 220.

The next scenario is when the IO 222 is received for the extent associated with the index 264. In this scenario, the bit 206 is a 1 and the bit 216 is a 0−(1,0). Because the bit 206 is a 1, this indicates that the extent associated with or identified by the index 264 in the primary bitmap 210 is included in the delta being generated. As a result, a copy on write is performed. More specifically, the bit 216 in the secondary bitmap 220 is marked or set to a 1 and the data in the relevant extent is read from the volume 224 and included in the delta. Then, the IO 222 is written to the volume 224 and the data previously read from the extent is transferred to a consumer (e.g., a replication appliance). Finally, the bit 206 is set to 0, indicating that the extent has been processed for the current delta operation. Once all of the marked bits in the primary bitmap have been processed and set to 0, the primary bitmap 210 is prepared to serve as the secondary bitmap during the next delta operation. When this occurs, the secondary bitmap 220 becomes the primary bitmap.

The next scenario is when the IO 222 is received for the extent associated with the index 266. In this scenario, the bit 208 is a 1 and the bit 218 is a 1−(1,1). This scenario should not occur and represents a consistency problem in which two overlapping IOs have been sent/received at the same time. It may not be possible to determine the order in which the overlapping IOs were generated. In this scenario, by way of example only, the previous IO may be allowed to finish and the next IO is then permitted.

Although the bit logic was illustrated with respect to four entries in the bitmaps, the bit logic is typically performed whenever the IO 222 is received during the process of generating a delta. More specifically, the bit logic is performed on the bits in the primary and secondary bitmaps associated with the address K of the IO 222 or otherwise impacted by the IO 222.

Advantageously, data included in a delta can be transferred in any order. More specifically, the bitmaps allow changes to data to be tracked with respect to non-overlapping extents on the volume 224. Thus, the order in which the data is read from the source or production volume 224 and transferred is not relevant. Further, the data's address is also transmitted such that the data can simply be applied to the target volume using the corresponding address.

More specifically, during a delta or transfer operation, the primary bitmap is scanned and data is stored in the extents of the volume corresponding to marked entries in the primary bitmap are transferred. IOs that are received during this delta operation are handled according to the bit logic discussed with respect to FIG. 2 .

FIG. 3 discloses aspects of a data protection system configured to perform data protection operations including delta operations. The data protection system, by way of example, may include the appliance 312, the filter 304, the primary bitmap 308, and or the secondary bitmap 310. The filter 304 may be implemented in the hypervisor of the virtual machine 302 and is able to intercept IOs from the virtual machine 302 to the volume 306.

FIG. 3 illustrates a virtual machine 302 (or physical machine, computing system, container) that may run an application. As IOs are generated (represented by IO 320), the IOs are transmitted to the volume 306 (or other storage). In this example, the filter 304 is configured to detect the IO 320 and then perform change block tracking using the address and size of the IO 320. Thus, the filter 304 may determine that the IO 320 is to be written to address K. The size allows the filter 304 to determine how many extents are affected by the IO 320. The entry or entries in the primary bitmap 308 are marked or changed from a 0 to a 1. In this example, a 1 indicates that the corresponding extent is dirty or needs to be backed up. This process continues until a request 316 or command to perform a delta operation is received. When an IO impacts multiple bits in the primary bitmap (e.g., address K, address K+1), the corresponding bits in the primary and secondary bitmaps are each considered independently as each may present a different scenario. The bit logic is applied to each pair of bits impacted by the IO because each pair may present a different scenario.

When the request 316 is received, the primary bitmap 308 is frozen with respect to IOs that occur after the request 316. The secondary bitmap 310 is used for IOs that happen after the request. Next, the primary bitmap 308 is processed in a single pass. The extents on the volume 306 corresponding to the marked entries in the primary bitmap 308 read from the volume 306 and are transferred to an appliance 312 as a delta 318. The delta 318, which typically includes a plurality of data corresponding to a plurality of extents, may also be transferred to cloud storage 314 or other target site. In one example, the target site is a cloud volume (e.g., a replica volume) that is configured to be like the volume 306. Thus, the extents in the delta 318, if desired, can be directly applied to the target volume regardless the order in which the data is received or packaged.

The primary bitmap 308 is processed in a single pass and only two bitmaps are required. This comparative reduction in complexity contributes to the ability to achieve an RPO on the order of seconds.

As the primary bitmap 308 is processed and extents corresponding to dirty bits are transferred in the delta 318, the corresponding entries in the primary bitmap are set to 0. Thus, once the delta operation has generated and transmitted the delta 318, all of the entries in the primary bitmap 308 are zero. At the same time, IOs are marked in the secondary bitmap. Thus, once the delta 318 has been transmitted, the secondary bitmap 310 becomes the primary bitmap and the primary bitmap becomes the secondary bitmap in preparation for the next request 316 to generate a delta.

FIG. 4 discloses aspects of a method for performing a delta operation. The method 400 may operate in the context of a virtual machine (physical machine, container, etc.) or an application therein is operating and sending IOs to a disk or volume. As IOs are generated and transmitted to the volume, the IOs are marked 402 in the primary bitmap. Thus, the primary bitmap identifies extents that have received writes or changes.

Next, a request to generate a delta is received and IOs subsequent to the delta request are marked in the secondary bitmap. Thus, the primary map is frozen with respect to a point in time and allows a backup to be generated for that point in time.

The primary bitmap is then processed 406 and changes since the last operation or data in the extents corresponding to marked bits in the primary bitmap are transmitted to a consumer, such as the appliance 312, and/or to a target site or device for storage.

Processing 406 the primary bitmap may include iterating the marked or dirty bits. As the primary bitmap is passed over, data in the extents corresponding to the marked bits is transmitted to a consumer along with the extent's address, index and/or IO address. When the read operation related to a particular entry in the primary bitmap is completed, that particular entry is set to 0 so that the extent will not be processed again for the current delta operation.

When an IO is received during transmission for an address K, bit logic is performed 408 for that address or index.

FIG. 5 discloses aspects of performing the bit logic. FIG. 5 discloses, more specifically, aspects of element 408 of the method 400. When a new IO is received for a location or extent being processed, referred to as an IO for address K in this example, the values of the bits in the primary and secondary bitmaps are evaluated. As previously described, there are four scenarios. For (0,0), the bit in the secondary bitmap for the address K is marked and the IO is allowed 504. For (0,1), the IO is simply allowed 506.

For (1,0), a copy on write 508 is performed. The copy on write 508 includes marking 510 the corresponding bit in the secondary bitmap. Then, data at the location or address on the volume or disk is read and sent 512, along with the address of the read, to a consumer. More specifically, data corresponding to the affected extents are transferred for inclusion in the delta being generated. The IO is then written 514 to the address or location and the bit in the primary bitmap is set 516 to 0.

For (1,1), this represents a collision where two IOs were sent to the same location in parallel. In this case, consistency may not be guaranteed. However, this situation can be avoided by proper programming in the application and in the IO stack. However, if the (1,1) scenario occurs, the method 400 waits for the bit in the primary bitmap to be set 516 to 0 for one of the IOs and the other IO is allowed to continue after the entry in the primary bitmap is set 516 to 0. More specifically, consistency is not guaranteed if the IOs actually overlap. This should be handled in the application or in the IO stack. However, two or more IOs may be directed to different portions of the same extent. Thus, the scenario of (1,1) can be handled as described. For the first IO, the copy on write is performed. The next IO can simply be allowed without performing the copy on write in this scenario.

When the primary bitmap is processed, the delta is completed 410 and transmitted to the consumer. The data associated with processing the primary bitmap may be transmitted as the data is read. A full delta may be assembled, if necessary, by the appliance or at another location. In one example, the delta is transmitted to the cloud storage or other target site.

Next, the roles of the bitmaps are switched 412. Thus, the secondary bitmap becomes the primary bitmap because incoming IOs are now being marked in the secondary bitmap. The primary bitmap becomes the secondary bitmap in anticipation of the next delta request.

Returning to FIG. 3 , the consumer (e.g., the appliance 316) is typically responsible for transmitting the delta 318 to its target such as a local storage device, a network file system, a remote target for replication or backup, or the like or combination thereof. The appliance 316 may be physical, virtual, containerized, or the like.

The frequency with which deltas are created may depend on the throughput generated by the virtual machine 302, the speed in which data can be read from the volume 306, and/or the rate at which data can be transferred to the target.

When throughput of the virtual machine 302 is high, the amount of data that needs to be read and transmitted for a delta operation increases. Because read and transfer rates are often in the range of hundreds of megabytes per second, reading and transferred should only take a few seconds, after which another delta may be generated.

Embodiments of the invention also provide a mechanism to control the rate at which data is transferred. More specifically, the appliance 312 can control the rate at which data is transferred to the appliance 312 particularly because the appliance 312 may be sensitive to the amount of data that can be efficiently handled due to processor or memory constraints. This helps the appliance 312 avoid situations where there is not enough time to evacuate the data in memory (e.g., due to not enough bandwidth, communication disruption, or the like. In this situation, data will accumulate in memory in the appliance 312 and there may be a need to limit memory usage. Alternatively, the appliance may have free resources and may be able to handle an increased rate. Thus, embodiments of the invention allow the appliance to control the transfer rate and resource consumption.

This can be achieved, in one example, using an acknowledge rate. With an acknowledge rate, the appliance 312 can control when an acknowledgement is transmitted to the filter 304. Delaying the acknowledge allows the appliance 312 to slow down the rate at which data is received at the appliance 312.

In another example, the primary bitmap may be processed using multiple or parallel streams rather than serially. The parallelism can be controlled by exposing a property/setting/configuration on the appliance 312, or by calling a function to return the target parallelism value. A value of 5 indicates that 5 regions can be sent in parallel.

Slowing down the rate of data transmission results in a longer transmission time and, as a result, the next delta may include more changes or more data. However, embodiments of the invention allow resources to be controlled and managed effectively.

Embodiments of the invention further relate to a data protection system that uses deltas and delta queues to provide near continuous data protection replication without snapshots or with reduced reliance on snapshots. Embodiments of the invention implement a delta based replication system with cadences on the order of seconds. Although the backups can be viewed as snapshots, the backups are achieved using deltas rather than snapshots. Further, deltas are distinct from journal systems, where the order of the IOs is important. Deltas may include multiple IOs whose order is not needed to generate the snapshot. Embodiments of the invention allow past and future point in time replicas to be stored and allow the replica to be moved or rolled to any available point in time.

FIG. 6A discloses aspects of an end-to-end replication or data protection system. In this example, a production virtual machine 602 is operating on a production site and may send IOs to a volume 606. The filter 604 operates as previously described such that the appliance 608 can send deltas (represented by the delta 610) to a target site. Thus, the appliance 608 and/or the filter 604 is an example of a data protection system that is configured to at least perform replication operations, which includes generating and sending deltas to a target site.

In this example, a replica virtual machine is operating or is present at the target or replica site. The appliance 612 or other receiver receives the delta 610 from the appliance 608. In some examples, there may be instances where the entire contents of the volume 606 is transferred to the replica site.

The appliance 612 receives the delta 610 and places the delta in the delta queue 624. In this example, the delta queue 624 includes a series of deltas, represented by delta 622 and 620 and/or a replica volume 618. A distributor 616 may be configured to read the delta queue 624 and apply the deltas in the queue 624 to the replica volume 618 if desired. Thus, when given a command or based on a cadence or frequency, the data protection system (e.g., the appliance 608 and/or the filter 604) may freeze a point in time at the volume 606 and transmit a delta to the appliance 612. When freezing the point in time, the secondary bitmap is used as previously described such that the primary bitmap, from which the delta is generated, represents the requested point in time.

When transmitting a delta, such as the delta 610, the appliance 608 receives data and metadata from the volume 606 in accordance with the marked entries in the primary bitmap. The metadata and the data are packaged as the delta 610 for transmission. Thus, all of the data and the metadata for a point in time constitute an example of a delta.

The delta queue 624 can be handled in different ways. For example, when a delta arrives at the replica site, the distributor 616 may immediately apply the delta to the replica volume 618. In this case, the replica volume 618 represents the latest point in time. Absent other backups, only the latest point in time is available at the replica site.

In another example, deltas can be stored in the delta queue 624. Maintaining the queue 624 ensures that multiple point in time copies are available or can be generated. In this example, the replica volume 618 represents the oldest available point in time and the most recently added delta (delta 622 in this example or the delta 610 when received by the appliance and placed in the queue 624) represents the newest point in time.

If a user wants to restore, recover, or use a particular point in time, the appropriate delta is selected from the queue 624. Once selected, the distributor 616 reads from the queue 624 and applies the deltas (oldest to newest) until the selected delta is reached and applied. The replica volume 618, at that point, corresponds to the selected or requested point in time.

FIG. 6B discloses aspects of how the deltas and the delta queue are structured or formatted. FIG. 6B illustrates the delta 620 from FIG. 6A, which is exemplary. The delta 620 may be formatted in different manners. Generally, the format 638 is an integrated format 626 where the data and the corresponding metadata are integrated. An example of integrated format is where the delta 620 includes a list of pairs, each pair including a location/address and the data—(location, data). Other metadata may also include the size of the IO. The location typically identifies the location of the extent.

Examples of the format 638 also include a separate format 628. In the separated format 628, the data and metadata are separated. The separated format 628 may include a list format. In the list format, a first list includes (location, pointer to data). The pointer to data points into a list/set of the data. Another separated format uses a bitmap to designate the data areas and an ordered list of data segments or extents that correspond to the set or dirty bits. Other formats are within the scope of embodiments of the invention.

The queue 624 may be implemented in multiple manners. The queue may be a RabbitMQ, Kafka, ActiveMQ or other public queues. For example, the queue 624 may be a block device 630 where the queue is managed by a receiver. The queue 624 may be implemented as a file system 632 or NAS (network attached storage) where the deltas are files with a naming convention or sequenced by a lookup file. The queue 624 may be implemented as object storage 634 and operate similarly to a file system. The queue 624 may also be implemented in secondary storage 636 if performance allows.

Returning to FIG. 6A, the data protection system also handles initializations and errors. Generally, the appliance 608 and/or the appliance 612 (or other component or part of the data protection system) may track the state of replication. the state is synchronized when, by way of example only, IOs have not been lost or the replica, at a point in time, matches the production volume at the same point in time. A state is unsynchronized when, by way of example, when the replica volume is not or cannot be made into a replica of the source volume.

For example, when the system is initially started, the replica volume 618 is not synchronized with the volume 606 until the contents of the volume 606 have been transferred to the replica volume 618. In one example, a basic initialization sequence is performed by marking all entries in the primary bitmap. If all entries in the primary bitmap are marked, all extents or segments are transferred. Thus, setting all bits in the primary bitmap results in the full volume 606 being sent to the replica volume 618. This may be sufficient for a first-time initialization and results in an initial synchronization. During initialization where the whole volume is read and transferred, the read rate may be controlled to ensure that the impact on production performance is controlled and not severely impacted.

If synchronization is later lost (e.g., a failure in the hypervisor which results in lost IOs), synchronization is needed. However, the synchronization may be performed more efficiently and elegantly. In one example, synchronization includes reading the volume 606 and the replica volume 618 in sections at, respectively, the source site and the replica site. The sections are hashed and only the hashes are sent across the network (e.g., hashes from the source are transmitted to the replica site) and compared. A match indicates that the data already exists at the replica site. In this manner, it is possible to identify unsynchronized sections and it is only necessary to transmit sections whose hashes do not match. The size of the sections can vary and may be selected based on overall size of the volume, time requirements, and computing resources needed to perform hashing/comparing related operations. If the contents of the source volume 606 and the replica volume 618 are close, the amount of data transferred for synchronization may be small, particularly compared to the entire volume size. In this manner, synchronization can be performed more quickly than transferring all contents of the source volume. After synchronization, data protection operations, including the generation of deltas and replication may resume.

Embodiments of the data protection system are capable of producing point in time copies in succession. This allows a continuous or near continuous snap mode to be enabled. In this example, each delta could correspond to a snapshot once reconstructed at the replica site. Referring to continuous snap mode reflects that deltas are generated and transmitted to a replica or target site.

In one example of a continuous snap mode, a delta is closed and transmitted, at which point another delta is immediately created (assuming there were changes to the volume). This indicates that the data protection system is not operating on a timer, but is simply creating as many snaps or deltas that can be transmitted. The deltas, at the target site can be reconstructed into full snapshots.

The cadence or RPO thus varies according to throughput of the production virtual machine and to the transfer rate. Higher throughput corresponds to the need to move more data and the time needed to move the data may depend on bandwidth.

However, embodiments of the invention are able to achieve an RPO of seconds. The time needed to transfer a delta is dependent on the time available to accumulate data during the transmission cycle. A recursive expression of the transfer time as a function of the previous cycle time can be created as illustrated below. BW=Bandwidth (MBs) TP=Virtual Machine Throughput (MBs) C=Compression Ratio t_(overhead)=Snap (delta) and communication overhead time (sec)

Using these definitions, a recursive time equation can be established as follows:

$t_{i} = {{\frac{C*TP}{BW}t_{i - 1}} + t_{overhead}}$

If the equation time t converges, it has an invariant convergence point as follows: t_(i)→t_(i−1)→t

The invariant point fort is as follows:

$t = \frac{t_{overhead}}{\left( {1 - \frac{C*TP}{BW}} \right)}$

This demonstrates that the time is a geometric series defined by the quotient Q as follows:

$Q = \frac{C*TP}{BW}$

The quotient Q is a ratio between the throughput of the virtual machine and the effective bandwidth. In this example, Q should be less than 1 to converge, which suggests that the average input rate is lower than the average output rate. In one example, a value of Q<0.5 may be used to ensure a swift convergence.

If

-   BW=100 MBs, -   TP=20 MBs, -   C=0.5, and -   t_(overhead)=2 secs, -   then Q=0.1, and -   t=2.22 secs.

In other words, the average PiT or delta time is 2.22 seconds. In other words a delta or snap can be generated every 2.22 seconds in this example.

Consider the convergence analysis in the context of initialization. This example demonstrates that the convergence occurs quickly even when a substantial amount of data is transferred, such as during the first-time initialization. In this example:

${V = {{Volume}{size}}}{R_{\max} = {\max{reading}{throughput}{without}{harming}{production}({MBs})}}{{{Initialization}{time}t_{0}} = {\max\left( {\frac{V}{R},\ \frac{C*V}{BW}} \right)}}$

The full volume sweep time is the slower of the read rate and the transfer rate. New data accumulates while initialization is occurring. The following illustrates when the cadence drops below 1 minute (deemed a time that is sufficiently fast).

${{Interations}{till}t} < {60{secs}\left( {{stable}{replication}} \right):n} > {{\log_{Q}\frac{60}{t_{0}}} + 1}$

Using the previous example values and including information that the volume size V is 200 GB and to is 1024 seconds, then:

${\log_{Q}\frac{60}{t_{0}}} = {{1.2}3}$

Thus, n=3 iterations. In this example, the cadence is under 60 seconds in three iterations, which includes a full sweep of the source volume. As a result, near continuous data protection cadences are possible with a wide range of parameters. These equations provide a tool to plan a system that ensures convergence and target a specific cadence time.

FIG. 7A discloses aspects of a delta queue. In FIG. 7B, a delta queue 720 is illustrated and includes a plurality of deltas, represented by deltas 704, 706, 708, and 710. The oldest point in time 702 is also illustrated. Each of the deltas 704, 706, 708, and 710 represent a point in time (a point of time is another way to reference a backup or a delta) and, as previously described, the deltas represent points in time spaced apart, in one example, on the order of seconds. Thus, the point in time 702 and the queue 720 represent near continuous data protection. Further, the queue 720 is ordered such that the delta 704 is the oldest delta, the delta 710 is the newest delta, and the delta 704 is closest in time to the point in time 702, which may be a replica volume.

As previously stated, a delta typically includes multiple segments or extents. An extent may include multiple segments. In this example, the delta 710 is associated with data 712, the delta 708 includes the data 714, the delta 706 includes the data 716, and the delta 704 includes the data 718.

In this example, the data 712 includes extents 2, 4, 6, and 10, the data 714 includes the extents 2, 5, 6, and 9, the data 716 includes extents 5, and 6, and the data 718 includes the extents 1, 2, and 3. As discussed with respect to FIG. 6B, the deltas may be stored such that the metadata is separate from the data. Thus, the metadata identifying the extents in the delta may be separate from the actual data in the extents.

When recovering to a point in time represented by a delta, it may be necessary to apply multiple deltas to the point in time 702. For example, if recovering or restoring the volume to the delta 710, the point in time replica volume can be recovered by applying the delta 704 to the volume 702, applying the delta 706 to the volume 702, applying the delta 708 to the volume 702 and finally applying the delta 710 to the volume 702.

In another example, the metadata of the deltas can be processed such that deltas are only accessed if necessary to restore the volume to the point in time of the delta 710. In this example, an examination of the metadata indicates that extent 2 is included in each of the deltas 710, 708, and 704. The extent 2 only needs to be applied to the volume 702 once and the version of the extent 2 applied to the volume 2 should be the newest with respect to the point in time being restored.

A similar analysis of the metadata results in the following actions. Extent 2, 4, 6, and 10 are applied from the delta 710. Extent 5 and 9 are applied from the delta 708, no extents are applied from the delta 706, and the extents 1 and 3 are applied from the delta 704.

FIG. 7B discloses aspects of batching to recover a point in time. The method 728 may begin by scanning 730 the metadata of the deltas being considered, which may include, inclusively, the deltas between the current volume and the selected point in time. The deltas being considered depends on the point-of-time selected for recovery. The set of affected areas or extents between the oldest point in time (the volume 702) and the requested point in time are accumulated 732. The metadata is processed to identify which extents should be applied. For example, a union may be applied to the metadata to identify unique extents. Then the method 728 iterates 734 from the target point in time (newest for this recovery operation) to the oldest delta. During the iteration, an extent (or segment) is applied to the replica volume only the first time the extent or segment is encountered.

A similar method may be done with delta metadata (even when integrated with the data) by applying operations such as unions, intersections, or subtractions in order to identify which extents to apply to the oldest point in time. Generally, the method 728 results in a system that applies from the newest point in time to the oldest rather than applying the oldest deltas first. This may allow the recovery operation to skip deltas entirely when appropriate or access less than all the extents or data of a delta. This makes the process of recovering to a selected point in time more efficient.

FIG. 8A discloses aspects of a data protection system configured to restore to future and past point in time replicas relative to a current point in time replica volume. FIG. 8A illustrates a delta queue 816 that can be accessed and processed by a distributor 802. In this example, the current volume 808 is at time T and represent a current volume or replica. The queue 816, however, has later in time deltas 804, 806 and undo deltas 810, 812. The queue 816 also illustrates the oldest undo delta 814. Thus, no deltas are available earlier in time than the delta 814.

In FIG. 7A, the ability to generate a newer PiT is unidirectional or forward looking. While FIG. 7A illustrated the ability to move a replica forward in time by applying deltas, which includes applying deltas in a batch manner, FIG. 8A illustrates the ability to move a replica forward and/or backward in time. The distributor 802 can thus generate a current volume for any point in time represented in the queue 816. By creating undo deltas, the current volume can be rolled forward or backwards as desired. In one example, the undo deltas may be placed in a separate queue.

The undo deltas 810, 812, and 814 may have a format similar to the format of the deltas 804 and 806, but with different content. For example, when rolling the current volume 808 from time T to time T+1, the locations of the data to be written from the delta 806 to the current volume 808 are known. This allows an undo delta to be created by reading the data on the current volume 808, which will be overwritten with the data from the delta 806, and writing that data to a new undo delta. The undo delta is inserted into the queue 816.

FIG. 8B discloses aspects of rolling a current volume forward using a delta queue. FIG. 8B illustrates that the current volume 808 has been rolled forward to time T+1 (now illustrated as current volume 818). Thus, the current volume 818 corresponds to time T+1 and a new undo delta 820 for time T has been created and inserted into the delta queue 816 at the appropriate location.

With reference to FIGS. 8A and 8B, the delta 820 was created by reading the data from the current volume 808 that was to be overwritten with data from the delta 806 and writing that data to the undo delta 820. The data from the delta 806 is then written to the current volume 808 to create the new current volume 818. Thus, the delta 806 is, in effect, the new current volume. The undo delta 820 allows the current volume to be rolled back from time T+1 to time T.

FIG. 8C illustrates an example of rolling the current volume from time T to time T−1. In this example and with reference to FIGS. 8A and 8C, the data in the current volume 808 to be overwritten using the data from the undo delta 810 is written to the delta 830. This in effect creates a delta for time T now that the current volume 822 corresponds to time T−1. In this case, however, the new delta 830 is inserted at the back of the forward looking portion of the delta queue 816. Data from the undo delta 810 is then written to the current volume such that the current volume 822 corresponds to time T−1.

FIG. 8D discloses aspects of a method for generating a point in time volume. The method of FIG. 8D assumes that a current volume exists and corresponds to a point in time. The associated queue also includes forward deltas and undo deltas. As a result, there may be forward looking deltas and backward looking or undo deltas in the delta queue. The forward deltas are typically forward looking or later in time relative to the current time of the replica volume. The undo deltas are backward looking or earlier in time relative to the current time of the replica volume. As the replica volume is rolled forwards or backwards, relative forward deltas or undo deltas are created such that the rolling can be reversed. When the forward deltas or undo deltas are created, they are inserted in the delta queue to be closest in time to the current replica volume. For example, when rolling forward one delta, the undo delta is inserted into the queue to be closest to the replica volume. When rolling forward multiple deltas, it may be necessary to create multiple forward deltas or undo deltas depending on the direction in which the replica volume is rolled—forwards or backwards. The method 838 discloses rolling the current volume to the next point in time and creating an undo delta such that the process can be reversed.

In this example, the metadata of a next delta is read 840. The metadata identifies the addresses or locations of data (the extents) associated with the next delta in the queue. Next, data (e.g., the extents to be replaced or overwritten) from the current volume is read 842 based on the metadata of the next delta. More specifically, an undo delta is created 844 by reading the data from the current volume based on the metadata from the next delta and writing that data and metadata to the new undo delta. Once the undo delta is created, the data from the next delta is read and applied 846 to the current volume. Thus, the current volume has been rolled forward from the current time to the next time.

FIG. 8E discloses aspects of rolling a current volume to a previous point in time using the delta queue. The method of FIG. 8E assumes that a current volume exists. As a result, there may be forward looking deltas and backward looking or undo deltas in the delta queue. The method 848 discloses rolling the current volume to a previous point (e.g., the next previous point relative to the time of the current volume) in time and creating a forward looking delta such that the process can be reversed.

In this example, the metadata of an undo delta is read 850. The metadata identifies the addresses or locations of data (e.g., extents) associated with the undo delta in the queue. Next, data from the current volume is read 852 based on the metadata of the undo delta. More specifically, a delta is created 854 by reading the data from the current volume based on the metadata from the undo delta and writing that data from the current volume (and its metadata) to the new delta. Once the delta is created, the data or extents from the undo delta is read and applied 846 to the current volume. Thus, the current volume has been rolled backward from the current time to the previous time.

When rolling the current volume backward/forward multiple points in time, it may be possible to generate the relevant forward looking deltas or the relevant undo deltas. This process could also be batched by examining all of the metadata of the relevant deltas or undo deltas. Thus, when the process is ready to write to the current volume to “move” it to another point in time, the relevant metadata from all intervening deltas or undo deltas can be batched as previously described. In one example, batching may unify the intervening deltas or undo deltas as applicable into one delta or one undo delta. Accumulating a set of extents in deltas affected by an operation is an example of batching and may include accumulating a set of extents from the affected deltas and processing the set of extents such that only the relevant extents are applied. For example, the newest extent in the affected deltas is applied.

In general, embodiments of the invention may be implemented in connection with systems, software, and components, that individually and/or collectively implement, and/or cause the implementation of, data protection operations which may include, but are not limited to, delta operations, differential operations, data replication operations, IO replication operations, data read/write/delete operations, data deduplication operations, data backup operations, data restore operations, data cloning operations, data archiving operations, and disaster recovery operations. More generally, the scope of the invention embraces any operating environment in which the disclosed concepts may be useful.

At least some embodiments of the invention provide for the implementation of the disclosed functionality in existing backup platforms, examples of which include the Dell-EMC NetWorker and Avamar platforms and associated backup software, and storage environments such as the Dell-EMC DataDomain storage environment. In general however, the scope of the invention is not limited to any particular data backup platform or data storage environment.

New and/or modified data collected and/or generated in connection with some embodiments, may be stored in a data protection environment that may take the form of a public or private cloud storage environment, an on-premises storage environment, and hybrid storage environments that include public and private elements. Any of these example storage environments, may be partly, or completely, virtualized. The storage environment may comprise, or consist of, a datacenter which is operable to service read, write, delete, backup, restore, and/or cloning, operations initiated by one or more clients or other elements of the operating environment. Where a backup comprises groups of data with different respective characteristics, that data may be allocated, and stored, to different respective targets in the storage environment, where the targets each correspond to a data group having one or more particular characteristics.

Example cloud computing environments, which may or may not be public, include storage environments that may provide data protection functionality for one or more clients. Another example of a cloud computing environment is one in which processing, data protection, and other, services may be performed on behalf of one or more clients. Some example cloud computing environments in connection with which embodiments of the invention may be employed include, but are not limited to, Microsoft Azure, Amazon AWS, Dell EMC Cloud Storage Services, and Google Cloud. More generally however, the scope of the invention is not limited to employment of any particular type or implementation of cloud computing environment.

In addition to the cloud environment, the operating environment may also include one or more clients (or modules, engines, filters, etc.) that are capable of collecting, modifying, transmitting, and creating, data. As such, a particular client may employ, or otherwise be associated with, one or more instances of each of one or more applications that perform such operations with respect to data. Such clients may comprise physical machines, virtual machines (VM), or containers.

Particularly, devices in the operating environment may take the form of software, physical machines, VMs, containers, or any combination of these, though no particular device implementation or configuration is required for any embodiment. Similarly, data protection system components such as databases, storage servers, storage volumes (LUNs), storage disks, replication services, filters, appliances and other consumers, backup servers, restore servers, backup clients, and restore clients, for example, may likewise take the form of software, physical machines or virtual machines (VM), though no particular component implementation is required for any embodiment.

As used herein, the term ‘data’ is intended to be broad in scope. Thus, that term embraces, by way of example and not limitation, data segments such as extents, blocks or such as may be produced by data stream segmentation processes, data chunks, data blocks, atomic data, emails, objects of any type, files of any type including media files, word processing files, spreadsheet files, and database files, as well as contacts, directories, sub-directories, volumes, and any group of one or more of the foregoing.

Example embodiments of the invention are applicable to any system capable of storing and handling various types of objects, in analog, digital, or other form. Although terms such as document, file, segment, block, or object may be used by way of example, the principles of the disclosure are not limited to any particular form of representing and storing data or other information. Rather, such principles are equally applicable to any object capable of representing information.

As used herein, the term ‘backup’ is intended to be broad in scope. As such, example backups in connection with which embodiments of the invention may be employed include, but are not limited to, full backups, partial backups, clones, snapshots, and incremental, delta, or differential backups.

It is noted with respect to the example method of Figure(s) XX that any of the disclosed processes, operations, methods, and/or any portion of any of these, may be performed in response to, as a result of, and/or, based upon, the performance of any preceding process(es), methods, and/or, operations. Correspondingly, performance of one or more processes, for example, may be a predicate or trigger to subsequent performance of one or more additional processes, operations, and/or methods. Thus, for example, the various processes that may make up a method may be linked together or otherwise associated with each other by way of relations such as the examples just noted. Finally, and while it is not required, the individual processes that make up the various example methods disclosed herein are, in some embodiments, performed in the specific sequence recited in those examples. In other embodiments, the individual processes that make up a disclosed method may be performed in a sequence other than the specific sequence recited.

Following are some further example embodiments of the invention. These are presented only by way of example and are not intended to limit the scope of the invention in any way.

Embodiment 1. A method comprising: selecting a delta from a delta queue, wherein the selected delta corresponds to a first point in time and wherein a replica volume corresponds to a second point in time, scanning metadata of affected deltas, the affected deltas including the selected delta and deltas in the delta queue between the selected delta and the replica volume, accumulating a set of extents from the metadata to be applied to the replica volume from the affected deltas, and iterating from the selected delta to the oldest delta in the affected deltas to move the replica from the second point in time to the first point in time by applying extents from the set of extents to the replica volume, wherein an extent is only applied when first encountered during the iteration.

Embodiment 2. The method of embodiment 1, wherein the metadata of the affected deltas and data of the extents are separated from each other, wherein the metadata comprises a list for each delta of a location of an extent and a pointer to the extent or includes a bitmap where each entry in the bitmap corresponds to an extent of the delta.

Embodiment 3. The method of embodiment 1 and/or 2, wherein accumulating the set of extents includes performing a union of the extents included in the affected deltas based on the metadata.

Embodiment 4. The method of embodiment 1, 2, and/or 3, accumulating the set of extents ensures that an extent present in more than one of the affected extents is only applied to the replica volume once.

Embodiment 5. The method of embodiment 1, 2, 3, and/or 4, wherein when an extent is present in more than one of the affected extents, only the newest extent is applied to the replica volume.

Embodiment 6. The method of embodiment 1, 2, 3, 4, and/or 5, wherein accumulating the set of extents prevents data of extents associated with a delta from being accessed when the same extent is present in a newer delta in the affected deltas.

Embodiment 7. The method of embodiment 1, 2, 3, 4, 5, and/or 6, further comprising receiving a delta at a receiver and inserting the delta into the delta queue.

Embodiment 8. The method of embodiment 1, 2, 3, 4, 5, 6, and/or 7, wherein the affected deltas are applied in order from newest to oldest.

Embodiment 9. The method of embodiment 1, 2, 3, 4, 5, 6, 7, and/or 8, wherein extents in each of the affected deltas are configured to be applied in any order.

Embodiment 10. The method of embodiment 1, 2, 3, 4, 5, 6, 7, 8, and/or 9, wherein accumulating the set of extents includes applying union and subtraction operations to identify redundant extents among the set of extents from the affected deltas.

Embodiment 11. A method for performing any of the operations, methods, or processes, or any portion of any of these, or any combination thereof disclosed herein.

Embodiment 12. A non-transitory storage medium having stored therein instructions that are executable by one or more hardware processors to perform operations comprising the operations of any one or more of embodiments 1 through 11.

The embodiments disclosed herein may include the use of a special purpose or general-purpose computer including various computer hardware or software modules, as discussed in greater detail below. A computer may include a processor and computer storage media carrying instructions that, when executed by the processor and/or caused to be executed by the processor, perform any one or more of the methods disclosed herein, or any part(s) of any method disclosed.

As indicated above, embodiments within the scope of the present invention also include computer storage media, which are physical media for carrying or having computer-executable instructions or data structures stored thereon. Such computer storage media may be any available physical media that may be accessed by a general purpose or special purpose computer.

By way of example, and not limitation, such computer storage media may comprise hardware storage such as solid state disk/device (SSD), RAM, ROM, EEPROM, CD-ROM, flash memory, phase-change memory (“PCM”), or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other hardware storage devices which may be used to store program code in the form of computer-executable instructions or data structures, which may be accessed and executed by a general-purpose or special-purpose computer system to implement the disclosed functionality of the invention. Combinations of the above should also be included within the scope of computer storage media. Such media are also examples of non-transitory storage media, and non-transitory storage media also embraces cloud-based storage systems and structures, although the scope of the invention is not limited to these examples of non-transitory storage media.

Computer-executable instructions comprise, for example, instructions and data which, when executed, cause a general purpose computer, special purpose computer, or special purpose processing device to perform a certain function or group of functions. As such, some embodiments of the invention may be downloadable to one or more systems or devices, for example, from a website, mesh topology, or other source. As well, the scope of the invention embraces any hardware system or device that comprises an instance of an application that comprises the disclosed executable instructions.

Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts disclosed herein are disclosed as example forms of implementing the claims.

As used herein, the term ‘module’ or ‘component’ or ‘engine’ may refer to software objects or routines that execute on the computing system. The different components, modules, engines, and services described herein may be implemented as objects or processes that execute on the computing system, for example, as separate threads. While the system and methods described herein may be implemented in software, implementations in hardware or a combination of software and hardware are also possible and contemplated. In the present disclosure, a ‘computing entity’ may be any computing system as previously defined herein, or any module or combination of modules running on a computing system.

In at least some instances, a hardware processor is provided that is operable to carry out executable instructions for performing a method or process, such as the methods and processes disclosed herein. The hardware processor may or may not comprise an element of other hardware, such as the computing devices and systems disclosed herein.

In terms of computing environments, embodiments of the invention may be performed in client-server environments, whether network or local environments, or in any other suitable environment. Suitable operating environments for at least some embodiments of the invention include cloud computing environments where one or more of a client, server, or other machine may reside and operate in a cloud environment.

With reference briefly now to FIG. 9 any one or more of the entities disclosed, or implied, by the Figures and/or elsewhere herein, may take the form of, or include, or be implemented on, or hosted by, a physical computing device, one example of which is denoted at 900. As well, where any of the aforementioned elements comprise or consist of a virtual machine (VM), that VM may constitute a virtualization of any combination of the physical components disclosed in FIG. 9 .

In the example of FIG. 9 , the physical computing device 900 includes a memory 902 which may include one, some, or all, of random-access memory (RAM), non-volatile memory (NVM) 904 such as NVRAM for example, read-only memory (ROM), and persistent memory, one or more hardware processors 906, non-transitory storage media 908, UI device 910, and data storage 912. One or more of the memory components 602 of the physical computing device 900 may take the form of solid-state device (SSD) storage. As well, one or more applications 914 may be provided that comprise instructions executable by one or more hardware processors 906 to perform any of the operations, or portions thereof, disclosed herein.

Such executable instructions may take various forms including, for example, instructions executable to perform any method or portion thereof disclosed herein, and/or executable by/at any of a storage site, whether on-premises at an enterprise, or a cloud computing site, client, datacenter, data protection site including a cloud storage site, or backup server, to perform any of the functions disclosed herein. As well, such instructions may be executable to perform any of the other operations and methods, and any portions thereof, disclosed herein.

The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope. 

What is claimed is:
 1. A method, comprising: selecting a delta from a delta queue, wherein the selected delta corresponds to a first point in time and wherein a replica volume corresponds to a second point in time; scanning metadata of affected deltas, the affected deltas including the selected delta and deltas in the delta queue between the selected delta and the replica volume; accumulating a set of extents from the metadata to be applied to the replica volume from the affected deltas, wherein each extent corresponds to a portion of a volume, wherein accumulating the set of extents includes performing a union of the extents associated with the affected deltas based on the metadata and wherein accumulating the set of extents ensures that an extent in the set of extents that is associated with one or more of the affected deltas is only applied to the replica volume once; and iterating from the selected delta to an oldest delta in the affected deltas to move the replica volume from the second point in time to the first point in time by applying extents from the set of extents to the replica volume, wherein extents in the set of extends that are repeated are only applied when first encountered during the iteration.
 2. The method of claim 1, wherein the metadata of the affected deltas and data of the extents in the set of extents are separated from each other, wherein the metadata comprises a list, wherein the list includes, for each of the deltas, a location of an extent and a pointer to the extent or wherein the list includes a bitmap where each entry in the bitmap corresponds to an extent.
 3. The method of claim 1, wherein accumulating the set of extents prevents data of an extent in the set of extents that is associated with a delta in the affected deltas from being accessed when the same extent associated with a newer delta in the affected deltas.
 4. The method of claim 1, further comprising receiving a next delta at a receiver and inserting the next delta into the delta queue.
 5. The method of claim 1, wherein the affected deltas are applied in order from newest to oldest.
 6. The method of claim 1, wherein extents in each of the affected deltas are configured to be applied in any order.
 7. The method of claim 1, wherein accumulating the set of extents includes applying a subtraction operation to identify redundant extents among the set of extents associated with the affected deltas.
 8. A non-transitory storage medium having stored therein instructions that are executable by one or more hardware processors to perform operations comprising: selecting a delta from a delta queue, wherein the selected delta corresponds to a first point in time and wherein a replica volume corresponds to a second point in time; scanning metadata of affected deltas, the affected deltas including the selected delta and deltas in the delta queue between the selected delta and the replica volume; accumulating a set of extents from the metadata to be applied to the replica volume from the affected deltas, wherein each extent corresponds to a portion of a volume, wherein accumulating the set of extents includes performing a union of the extents associated with the affected deltas based on the metadata and wherein accumulating the set of extents ensures that an extent in the set of extents that is associated with one or more of the affected deltas is only applied to the replica volume once; and iterating from the selected delta to an oldest delta in the affected deltas to move the replica volume from the second point in time to the first point in time by applying extents from the set of extents to the replica volume, wherein extents in the set of extends that are repeated are only applied when first encountered during the iteration.
 9. The non-transitory medium of claim 8, wherein the metadata of the affected deltas and data of the extents in the set of extents are separated from each other, wherein the metadata comprises a list, wherein the list includes, for each of the deltas, a location of an extent and a pointer to the extent or wherein the list includes a bitmap where each entry in the bitmap corresponds to an extent.
 10. The non-transitory of claim 8, wherein accumulating the set of extents prevents data of an extent in the set of extents that is associated with a delta in the affected deltas from being accessed when the same extent associated with a newer delta in the affected deltas.
 11. The non-transitory medium of claim 8, further comprising receiving a next delta at a receiver and inserting the next delta into the delta queue.
 12. The non-transitory medium of claim 8, wherein the affected deltas are applied in order from newest to oldest.
 13. The non-transitory medium of claim 8, wherein extents in each of the affected deltas are configured to be applied in any order.
 14. The non-transitory medium of claim 8, wherein accumulating the set of extents includes applying a subtraction operation to identify redundant extents among the set of extents associated with the affected deltas. 